This invention relates to an optical wavelength division multiplexing (WDM) add/drop arrangement.
In a long-haul, high-capacity wavelength division multiplexing (WDM) optical network, the capability to remove and replace selective WDM wavelengths at multiple add/drop nodes across the network is essential for a variety of value-added communication services. Such communication services include local access, interactive multimedia and wavelength leasing. In particular, this capability requires adding or dropping one or more optical wavelengths (also known as channels) at each add/drop network node from a multiwavelength-multiplexed signal as well as substituting one or more optical wavelengths with new optical wavelengths.
WDM add/drop systems have been disclosed in the prior art. Such systems have been constructed by pairing two waveguide grating routers (WGR), the first a 1xc3x97N wavelength demultiplexer and the second a Nxc3x971 passive wavelength combiner or multiplexer. In addition, an array of optical switches operate on a subset of the N wavelength interconnections between these two WGRs to remove, add and replace selective optical wavelengths (a system of this sort is disclosed in U.S. Pat. No. 5,526,153, entitled xe2x80x9cOptical Channel Adding/Dropping Filterxe2x80x9d, issued to Glance on Jun. 11, 1996). In such a system, a multiwavelength-multiplexed signal is first demultiplexed, in the first WGR (e.g., the demultiplexer) to yield a multiplicity of individual optical wavelengths. Thereafter, a subset of the demultiplexed optical wavelengths is directed to the optical switches where either a drop, add, or a drop and add of one or more of the individual optical wavelengths takes place. Subsequently, the individual wavelengths are directed to the second WGR (e.g., the multiplexer) to produce a new multiwavelength-multiplexed signal. The optical multiplexers and demultiplexers used in such add/drop systems are further described in U.S. Pat. No. 5,002,350, entitled xe2x80x9cOptical Multiplexer/Demultiplexerxe2x80x9d, and U.S. Pat. No. 5,136,671, entitled xe2x80x9cOptical Switch, Multiplexer, and Demultiplexerxe2x80x9d both issued to Dragone on Mar. 26, 1991 and Aug. 4, 1992, respectively.
Although such WDM add/drop systems are effective for dropping and adding wavelengths, they add significant cost to optical networks since they require an array of expensive optical switches. With increased market competition and heightened customer expectations, it has become important to develop a low-cost WDM add/drop system.
An optical wavelength division add/drop multiplexer (WADM) arrangement in accordance with the principles of the present invention includes a pair of optical routers, such as waveguide grating routers (WGRs), wherein at least one of the optical routers includes a duplicated plurality of input or output waveguides. Certain waveguides associated with each optical router are coupled together and at least one attenuator-switch, such as a micro-electromechanical system (MEMS) optical shutter, is interconnected between the coupled waveguides.
In one illustrative embodiment, the WADM arrangement includes two duplicated-port waveguide grating routers (DWGR) and a plurality of optical shutters. The first DWGR is configured as a 1xc3x972N demultiplexer, which demultiplexes an optical multiplexed signal into a duplicated plurality of channels. The other DWGR is configured as a 2Nxc3x971 multiplexer. Each DWGR includes a duplicated plurality of input or output waveguides, wherein respective pairs of each duplicated plurality of waveguides have substantially identical spectral filtering characteristics. The first plurality of output waveguides of the first DWGR, which are coupled to the first plurality of input waveguides of the second DWGR, propagate one of the duplicated plurality of channels. Optical shutters are inserted between respective waveguides of these two pluralities of waveguides and can be used to block or reflect incident optical wavelengths corresponding to channels to be terminated at the node where the WADM arrangement is provided. The second plurality of output waveguides in the first DWGR propagate the other duplicated plurality of channels and drop these channels at the node where the WADM arrangement is provided. Lastly, the second plurality of input waveguides in the second DWGR are for adding channels to provide full add/drop capability. Once all of the appropriate adds/drops are accomplished, the channels propagating in the first and second input waveguides are multiplexed by the second DWGR. Thus, in addition to conventional add/drop capability, the WADM arrangement has a so-called xe2x80x9cdrop and continuexe2x80x9d functionality, wherein channels are both dropped at a particular node and may also continue to further nodes in an optical network.
In contrast with the prior art, the present invention, by virtue of the DWGRs and a unique configuration, achieves add/drop as well as drop and continue functionality while reducing the cost of conventional WADM nodes in optical networks. The optical switches used in typical WADM nodes are not needed; the optical shutters that are present in this invention are much less expensive.